Lf U-14CjMethionine fed to apple tissue was efficiently converted to ethylene when the tissue was incubated in air. In nitrogen, however, it was not metabolized to ethylene but was instead converted to 1-aminocyclopropane-1-carboxylic acid (ACC). When apple tissues were fed with L[methylI4Cjmethionine or L{35S~methionine and incubated in nitrogen, radioactivity was found subsequently in methylthioribose. This suggests that methionine is first converted to S-adenosylmethionine which is in turn fragmented to ACC and methylthioadenosine. Methylthioadenosine is then hydrolyzed to methylthioribose. The conclusion that ACC is an intermediate in the conversion of methionine to ethylene is based on the following observations: Labeled ACC was efficiently converted to ethylene by apple tissue incubated in air; the conversion of labeled methionine to ethylene was greatly decreased in the presence of unlabeled ACC, but the conversion of labeled ACC to ethylene was little affected by the presence of unlabeled methionine; and 2-amino-4(2'-aminoethoxy)trans-3-butenoic acid, a potent inhibitor of pyridoxal phosphate-mediated enzyme reactions, greatly inhibited the conversion of methionine to ethylene but did not inhibit conversion of ACC to ethylene. These data indicate the following sequence for the pathway of ethylene biosynthesis in apple tissue: methionine -_ S-adenosylmethionine -ACC -ethylene. A possible mechanism accounting for these reactions is presented. Ethylene is a plant hormone that initiates fruit ripening and regulates many aspects of plant growth and development (1). It is generally thought that methionine is the common precursor of ethylene throughout diverse higher plant tissues in which the hormone occurs and exerts its many effects (2-4). In apple tissue the conversion of methionine to ethylene represents the major metabolism of methionine (5). In this conversion, C-1 of methionine is converted to CO2, C-2 to formic acid, and C-3,4 to ethylene. The sulfur atom, however, is retained in the tissue (2). Because the conversion of methionine to ethylene is greatly inhibited by uncouplers of oxidative phosphorylation, Burg (6) and Murr and Yang (7) proposed that S-adenosylmethionine (SAdoMet), formed from methionine and ATP, is an intermediate between methionine and ethylene. Adams Feeding Experiments. Plugs, 1 cm in diameter and 2 cm long, were cut from apple fruit with a cork borer and scalpel. They were quickly rinsed in 2% (wt/vol) KC1 and blotted with a paper towel. Indicated substrates were infused by a vacuum infiltration technique as described (11). For incubation in a nitrogen or air atmosphere, a tissue plug was placed in a 12-ml plastic syringe fitted with a three-way stopcock. Two holes (3 mm diameter) were made near the end of the syringe to allow flushing with a stream of nitrogen or air from the stopcock inlet.After flushing, the syringe was sealed for incubation. Gas samples were withdrawn periodically from the incubation syringe with a sampling syringe and assayed for total and rad...

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I-Aminocyclopropaae-l-carboxylic acid (ACC) level, ACC synthase activity, and ethylene production in cucumbers (Cacwmis sativus L.) remain low while the fruit are held at a temperature which causes chillin jury (2.5°C) and increase rapidly only upon transfer to warmer temperatures. The increase in ACC synthase activity during the warming period is inhibited by cycloheximide but not cordycepin or a-amanitin. Our data indicate that the synthesis of ACC synthase, which results in increased ACC levels and accelerated ethylene production, occurs only upon warming, possibly from a message produced or umnasked during the chillg period. Ethylene production by chflled (2.5'C) cucumbers increased very little upon transfer to 250C if the fruit were chilled for more than 4 days. The fruit held for 4 days or longer showed a large increase in ACC levels but little ethylene production even in the presence of exogenous ACC. This suggests that the system which converts ACC to ethylene is damaged by prolonged exposure to the chilling temperature. Cucumbers stored at a low but nonchiling temperature (13°C) showed very little change in ACC level, ethylene production, or ACC synthase activity even after transfer to 25°C.Low-temperature stress induces ethylene production from plant tissues which do not normally produce significant amounts of ethylene (1,8,13,20,21,24). Our previous study (21) showed that the pathway for ethylene biosynthesis in chilled cucumbers (Cucumis sativus L.) is similar to that in ripening fruits. Furthermore, the increased ethylene production by chilled cucumbers appeared to be a result of an increased capacity of the tissue to make ACC2; the synthesis of ACC was identified as the step stimulated by chilling (21) and higher ACC levels were found in tissues after exposure to the chilling temperature. Since the ethylene production and ACC levels in our previous study were not measured until after the fruit were transferred to warmer temperatures, it was not known whether the stimulation of ACC synthesis and ethylene production occurred during the chilling period or took place during warming. Although prolonged chilling caused a large increase in ACC levels, the fruit exhibited reduced ethylene production even after they were allowed to warm (21), suggesting that prolonged chilling damages the system which converts ACC to ethylene. The synthesis of ACC has been shown to be the rate-limiting step in ethylene biosynthesis in several plant tissues (3, 7, 16). ACC synthase, which catalyzes the conversion of SAM to ACC, has been studied in tomato fruit tissue by Boiler et aL (4) and Yu et aL (25), and the amount of that enzyme has been implicated as the controlling factor for ethylene production in apple cell suspension cultures (2). The present study was undertaken to determine ACC levels and ACC synthase activity during chilling and upon warming in order to characterize the kinetics and timing of chilling-induced ethylene production in cucumber fruit. MATERIALS AND METHODSPlant Materials. Cucumbers (Cucumi...

The intensity of astringency of red wine increases when a single wine is sipped repeatedly or during evaluation of several red wines in one session. The effectiveness of different rinses in reducing or preventing the build‐up of astringency was evaluated using time‐intensity (TI) methodology. Trained subjects continuously rated the intensity of an astringent red wine using a sip and spit protocol. Ten s after the wine was sipped, it was expectorated. Ten s later, a rinse was sipped, which was spat out after another 10 s. Judges rated until astringency was no longer perceived. Between wine‐rinse combinations, subjects rinsed twice with de‐ionised water for 20 s. Intensity ratings at maximum intensity and at 5 s intervals were extracted from the TI curves and subjected to analysis of variance. Pectin (1 g/L) reduced astringency more effectively than water, polyvinylpyrrolidone (PVP) (4 g/L), gelatin (6 g/L), or ovalbumin (4 g/L) (Experiment 1). Low (1g/L) and high (5 g/L) concentrations of pectin and a high (1 g/L) concentration of carboxymethylcellulose (CMC) decreased astringency significantly more than rinses of Polycose, (5 and 40 g/L), CMC (0.01 g/L) or water (Experiment 2). In a third Experiment, unsalted crackers were shown to be more effective in decreasing astringency than water, although the pectin (5 g/L) rinse was superior to crackers and water. For the inter‐stimulus rinse protocol to be most effective, it was found to be important to remove the residuals from each ‘rinse’ by extensive water rinses before tasting the next wine.

Ethylne production in mung bean hypocotyls was greatly increased by treatment with 1-am_iocyckloopane-l-carboxylic acid (ACC), which was utilized as the ethylee precursor. Unlike auxin-stimulated ethylene production, ACCdependent ethylene production was not inhibited by aminoethoxyinylglycine, which is nown to inbibit the conversion of S-adenosyhnethionine to ACC. While the conversion of methionine to ethylene requires induction by auxin, the conversion of neine to S-adenosylmethionine and the conversion of ACC to ethylene do not. It is prposd that the conversion of S-adenosylmethionine to ACC is the rate-limiting step in the biosynthesis of ethylene, and that auxin stimulates ethylene production by inducing the synthesis of the enzyme involved in this reaction.Ethylene is an endogenous plant hormone which regulates many aspects of plant growth and development (1). In vegetative tissues the ethylene production rate is regulated by the internal levels of auxin (1) and methionine is thought to be the precursor of ethylene, as in other plant tissues (3, 12, 13). The ethyleneproducing system of auxin-treated vegetative tissues resembles that of climacteric fruit tissue in many aspects (9-11). Adams and Yang (2) recently studied ethylene biosynthesis in apple tissue and established the following biosynthetic sequence: methionine -+ SAM2 --* ACC --C2H4. It was shown that the conversion of SAM to ACC is sensitive to AVG inhibition. The present investigation was undertaken to determine which step in the metabolic pathway of ethylene biosynthesis is regulated by auxin in mung bean hypocotyls. MATERIALS AND METHODS

2,4-Dinitrophenol (DNP) and high temperature (35 to 40 C) are known to inhibit C2H4 production in various plant tissues. The present study was made to determine the step in the C2H4 biosynthetic pathway (methionine -* S-adenosylmethionine ISAMI -p 1-aminocyclopropane-1-carboxylic acid IACCI -* C2HM) at which these treatments exert their inhibitory effect. In mung bean hypocotyls the dose-inhibition curves for the effect of DNP on auxin-dependent C2H4 production (in which auxin exerts its effect by stimulating the conversion of SAM to ACC) and on ACC-dependent C2H, production (in which ACC is directly utilized as precursor) were similar. It was concluded, therefore, that DNP at low concentrations (below 50 micromolar) exerted its effect primarily on the conversion of ACC to C2H4, a step which is common to both systems. This view was further substantiated by quantitative analysis of the intermediates in the biosynthetic sequence. DNP exerted little influence on the content of SAM but caused a significant increase in the ACC content and marked inhibition in C2H4 production, indicating that the conversion of ACC to C2H4 is the crossover point. At higher concentrations (above 100 micromolar), DNP inhibited the conversion of methionine to ACC and to C2H4, and this effect could be attributed to the inhibition of SAM synthesis.The optimal temperature for maximal C2H4 production by apple tissue and mung bean hypocotyl is about 30 C. An increase in temperature to 35 C caused an accumulation of endogenous ACC, whereas C2H4 production was greatly reduced. These results suggest that the conversion of ACC to C2H4 is highly vulnerable to high temperature inhibition.C2H4 is a plant hormone which regulates many aspects of plant growth and development (1). In plant tissue the C2H4 production rate is regulated by various physiological and environmental factors. In 1960, Burg and Thimann (9) reported that DNP2 was an effective inhibitor of C2H4 production in apple tissue. Similar observations were reported for other fruit tissues and for auxininduced C2H4 production in vegetative tissues (7,15,20 (12) reported that pear fruits stopped production of C2H4 and failed to ripen when held at 40 C. In avocado, Eaks (10) found typical respiratory climacteric patterns occurring from 20 to 35 C. The respiratory climacteric maximum increased, but maximum C2H4 production decreased as the temperature increased from 25 to 40 C. Only trace amounts of C2H4 were produced at 35 C even though the tissue still showed a typical climacteric pattern. Although C2H4 production is more vulnerable to high temperature inhibition than is respiratory activity (8,10,18), the mode of the high temperature effect on C2H4 production has not been elucidated.Adams and Yang (4) have elucidated the C2H4 biosynthetic pathway in apple tissue as follows: methionine -+ SAM -. ACC --C2H4. This pathway has since been shown to be operative in auxin-induced C2H4 production in vegetative tissue (24) and other stress systems (21,25). The present investigation was undert...

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